How To Use An Audio Compressor In Your Church Sound System

How To Use An Audio Compressor In Your Church Sound System

Audio compressors are very powerful processing tools, yet they are often misunderstood and overlooked by volunteer church sound operators, who could really benefit from them. In this two-part article, we will cover why you would want to use a compressor and how to use one. This first article explains what you need to know in order to use one on the Pastor's microphone.

The pro audio world uses compression more than any other form of signal processing because it makes the music or message you are trying to convey easier to listen to, more consistent and improves intelligibility. If you listen to a radio broadcast or television show, you will notice that the sound is very consistent and smooth. Listen closely and you will hear that most of the dialog fluctuates very little in volume but it still sounds natural. There aren't times when you can't hear what is being said and there aren't times when a screaming voice is splitting your eardrums. The compressor can create this nice consistent sound by reducing the dynamic range of the audio program.

What is dynamic range? It is the range from the quietest sound to the loudest sound in the audio you are listening to. An example of something with a wide or large dynamic range would be an orchestral piece of music. There may be whispery quiet passages on just flutes or strings, and moments later, thundering waves of sound as the entire orchestra dives into a new movement. That's exciting, but not necessarily the kind of experience you want when listening to a sermon or teaching.

A compressor reduces (or compresses) the dynamic range by reducing the loudest sounds. Once you have reduced the dynamic range you can raise the overall system volume a bit without fear of it suddenly getting too loud or damaging your speakers. Bringing up the overall volume will also have the effect of bringing up the quietest portions of audio so it is more clearly understood in the midst of background sounds such as coughing, children and ventilation systems. Reducing the dynamic range can also mean that you don't have to 'ride the faders' or adjust the sound to fluctuations in a presenter's voice as often.

Compression can be used on individual sound sources (like the individual channels on your mixer) or on an entire mix of sounds (like the output of your mixer). Since we are talking about compression on the Pastor's mic, we will look at how to apply it to one channel of your mixer. Audio compressors can process one or multiple channels of audio depending on their design. The most common consist of two channels that can operate as two separate compressors or as a stereo unit. Since our first application is the pastor's microphone, we will look at only one channel in single mode. Whether your pastor uses the popular Countryman E6i ear-worn headset microphone, a lapel or a pulpit microphone you can benefit from adding a compressor to his signal chain.

Connection:
The most common way to connect a compressor to a mixer channel is through the channel insert jacks on the mixer using an insert cable which is commonly a cable with two "mono" phone plugs (Tip/Sleeve) to go to the Input and Output jacks of the compressor and one "stereo" (Tip/Ring/Sleeve) phone plug to go to the Insert jack on the Pastor's Input channel on your mixer. The cable will have labels to show which phone plug is for input and which is for output. (Some insert cables have XLR connectors instead of phone plugs, but these are much less common.)

With the compressor connected to the pastor's microphone channel we are ready to look at the compressor's features and talk about how to use them. We'll use the popular dbx 266XL Compressor 2-channel compressor as our example.



Since we will only be using one channel for our purpose, we've zoomed in on channel 2 in the image above. There are two parts of the channel. Outlined in red is the expander gate which can be used to reduce background noise in the channel when no one is talking. We are not going to cover the expander gate in this article, but it can be very useful (refer to your manual for more information). If you have a similar feature on your compressor set it to off unless you have learned how to properly set this feature. We outlined the compressor part of the channel in gold. We have also zoomed in on this section to better show the controls.



First, let's talk about each control. We'll give you suggestions for how to create the right settings at the end of this article.

Threshold:
Starting at the left, the first control knob is the threshold. The threshold sets the point or audio level that the compressor will start controlling the volume. The settings range from -40 db to +20 db, we placed red arrows to indicate the most likely range for our application. The final setting will depend on the pastor and the input sensitivity of the mixer channel. We will assume the sensitivity (trim) control on the mixer channel is set correctly. See the mixer owner's manual for an explanation on this setting if you experience results different than we describe below.

Soft Knee Compression:
This unit has a feature called over-easy, and sometimes referred to as soft knee compression. It makes the compression less detectable by starting gradually, so we recommend using it as indicated on the above compressor image. The diagrams on the right show how much the gain or volume will change once the signal reaches the threshold level based on the ratio settings. Notice the smooth transition from the point at which the compression starts to change the gain of the signal when utilizing the Over-Easy compression setting.

Compression Ratio:
The next control knob on the compressor is the Ratio, which determines the amount of gain reduction on the signal once it is greater than the threshold. The diagrams show the results of different ratio settings. For example, the 1:1 setting will do nothing to the signal, but the more you turn the knob clock wise, the more drastically it will decrease the volume of the audio that exceeds the set threshold point. If you set the control all the way to the right it will severely affect the signal to where it is acting as a hard limiter, not allowing the volume to reach over the threshold point. This can start to sound unnaturally squeezed or flattened.

Auto Attack and Release:
The attack and release controls determine how fast the compression starts or stops when the signal passes the threshold in either direction. You will note that we have drawn lines through both of these controls in our compressor image and recommend you select the automatic feature found on the dbx 266XL and many other audio compressors. This will automatically adjust the attack and release and is acceptable for this application.

Finding the right settings:
With both the over-easy/soft knee and the auto attack and release on, set the compression ratio at 2:1 and the threshold at 0db. Next we need to have a sound check with the pastor speaking as he does during his sermon. Remember, if he generally has a wide range from subtle to attention getting, make sure that you cover all those ranges during this sound check. Bring the threshold down (counter-clock wise) to -10 db or more and see if your gain reduction meter is showing any gain reduction. If so, how much and what has changed with the sound? Your goal is to lower the volume on the loudest portions of the audio and smooth out the sound of the Pastor's voice. On the right hand side of the compressor is the Output Gain, use this to add back the amount of volume that the threshold setting took away. This will bring up the volume on the quieter parts of the audio making your Pastor's voice more consistent and easy to hear.

The higher the ratio and the lower the threshold the more you will squish the sound. Too low a threshold or too high a ratio is not good, but experimenting to get the feel of how it works will help you get the results that sound best with your system in your space. Common settings are in the ranges pointed out by the red arrows in the dbx 266Xl Compressor Image.

Team Awareness:
The last thing to be concerned with is after you get these settings done you can still control the overall volume of the pastor's microphone with the channel volume control on the mixer. Be careful that you leave the channel sensitivity setting alone once you have your compressor set. Changing channel gain will change the level going into the compressor, changing how effective it will be on the pastor's voice. Make sure to share this process with your entire team. We recommend practicing this setup with your team prior to the sound check with the pastor if possible. This will be helpful if everyone is on the same page and able to make adjustments for guest speakers when needed.